Device for generating variable output voltage

ABSTRACT

A monostable multivibrator is connected to the input of a device for generating a variable output voltage, in which the output voltage derived from the source of a MOS field-effect transistor is varied in response to the variation of a voltage across a capacitor connected to the gate of the field-effect transistor. The output voltage may be increased and decreased stepwise.

United States Patent Minami et al.

[451 July 8,1975

DEVICE FOR GENERATING VARIABLE OUTPUT VOLTAGE Inventors: Shunji Minami;Shunzo Oka;

Takehide Takemura, all of Osaka,

Japan Assignee: Matsushita Electric Industrial Co.,

Ltd., Japan Filed: Dec. 14, 1973 Appl. No.: 424,647

Foreign Application Priority Data Dec. 20, 1972 Japan 47-128492 Dec. 20,1972 Japan 47-147212 Dec. 20, 1972 Japan 47-147213 US. Cl. 307/227;307/273; 307/304;

307/246 Int. Cl. H03k 4/02 Field of Search 307/233, 273, 227, 225,

[56] References Cited UNITED STATES PATENTS 2,999,208 9/1961 Ruehlemann328/186 X 3,105,158 9/1963 Nichols 307/227 3,333,111 7/1967 Houle307/273 3,571,620 3/1971 Hansen 307/233 Primary ExaminerStanley D.Miller, Jr. Attorney, Agent, or FirmBurgess, Ryan and Wayne [5 7]ABSTRACT A monostable multivibrator is connected to the input of adevice for generating a variable output voltage, in which the outputvoltage derived from the source of a MOS field-effect transistor isvaried in response to the variation of a voltage across a capacitorconnected to the gate of the field-effect transistor. The output voltagemay be increased and decreased stepwise.

4 Claims, 8 Drawing Figures SHEET PATH-HEB JUL 8 ms FIG.

TIME

OUTPUT VOLTAGE SHEET 3 FIG. 5

NUMBER OF SWITCH CLOSING LL] 2 -TIME '3 O PEG.

LL! (9 B 9 1- I.) D. D O

l 2 3 2 3 W 1 NUMBER OF NUMBER OF swwcmw) SWITCH(57) CLOSING M CLOSINGDEVICE FOR GENERATING VARIABLE OUTPUT VOLTAGE BACKGROUND OF THEINVENTION The present invention relates to a device for generating avariable output voltage of the type in which a voltage across acapacitor connected to the gate of a MOS field-effect transistor iscontrolled in response to a pulsatory voltage generated by a monostablemultivibrator so that the output voltage derived from the source of theMOS field-effect transistor may be varied stepwise.

In general, variable resistors have been widely used in order to vary avoltage, but they have the objectionable feature in that noise isproduced because the armature slides over the resistor element.Furthermore, the variable voltage obtained by the variable resistor isnot stable because the characteristics of the resistor element tend tobe greatly affected by the environmental temperature.

SUMMARY OF THE INVENTION One of the objects of the present invention istherefore to provide a device for generating a variable output voltagewhich eliminates the use of a variable resistor, but may accomplishprecisely the function of the variable resistor.

Another object of the present invention is to provide a device capableof increasing stepwise a DC output voltage.

A further object of the present invention is to provide a device capableof increasing stepwise an output voltage and of dropping the outputvoltage to zero when it reaches a predetermined level.

A still further object of the present invention is to provide a devicewhich may increase stepwise an output voltage when one switch is closedand may decrease stepwise the output voltage when the other switch isclosed.

Briefly stated, according to the present invention, a non-polarizedcapacitor is inserted between ground and the gate of a MOS field-effecttransistor, and the gate is connected through an input resistor and aneon bulb to a monostable multivibrator whose operation is controlled bya switch. Whenever the switch is closed, the output voltage is increasedstep by step. Furthermore, the output voltage may be returned to zeroafter it has reached a predetermined level. Moreover, the output voltagemay be increased stepwise when a switch of a first monostablemultivibrator is closed, and may be reduced also stepwise when a switchin a second monostable multivibrator is closed. Therefore, the devicesof the present invention are very advantageous when used with a circuitadapted to control the intensity of a lamp.

The devices of the present invention may eliminate the use of anarmature or brush and a resistor element of a conventional variableresistor, and may exactly accomplish the function of a variableresistor. Therefore, the noise problem may be overcome, and the agingproblem caused by the sliding contact of the armature with the resistorelement may be eliminated.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description ofsome preferred embodiments thereof taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a circuit diagram of a firstembodiment of the present invention;

FIGS. 2 and 3 are graphs used for the explanation thereof;

FIG. 4 is a circuit diagram of a second embodiment of the presentinvention;

FIG. 5 is a graph used for the explanation thereof;

FIG. 6 is a circuit diagram of a third embodiment of the presentinvention; and

FIGS. 7 and 8 are graphs used for the explanation thereof. 7

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

First Embodiment, FIGS. 1, 2, and 3 The base of a transistor 3 of amonostable multivibrator generally indicated by 2 is connected through aresistor 4 and a switch 1 to a power source 5. A resistor 6 connects thejunction between the switch 1 and the resistor 4 to ground. The base ofthe transistor 3 is also connected through a resistor 7 to the collectorof the other transistor 8 of the multivibrator 2, and the collector ofthe transistor 3 is connected through a capacitor 9 to the base of thetransistor 8. The emitters of both transistors 3 and 8 are grounded, andtheir collectors are connected through resistors 10 and 12,respectively, to a positive DC power source +V The base of transistor 8is also connected through a resistor 11 to the source +V The collectorof the transistor 8 is also connected through a neon bulb 13 and aninput resistor 14 to the gate of a MOS field-effect transistor 15. Anon-polarized capacitor 16 connects the gate of the field-effecttransistor 15 to ground, while the source of the field-effect transistoris grounded through an output resistor 17 and is connected to an outputterminal 18. The drain of the field-effect transistor 15 is connected toa DC source +V Next the mode of operation will be described hereinafter.When the switch 1 is turned off, the transistor 8 is conducting so thatits collector voltage becomes substantially zero. Therefore, the neonbulb 13 is not conducted. When the switch 1 is closed, the current flowsinto the base of the transistor 3 through the resistor 4 so that thetransistor 3 conducts. The collector potential of transistor 3 at thistime is substantially zero so that the base potential of the transistor8 is also substantially zero. As a result, the transistor 8 is turnedoff so that its collector voltage rises to a level almost equal to thevoltage +V thereby exceeding the firing potential of the neon bulb 13and causing it to conduct. The base potential of the transistor 8gradually rises with a time constant which is dependent upon the valuesof the capacitor 9 and the resistor 11, and finally the transistor 8 isturned on. Then, the collector potential drops substantially zero sothat the neon bulb 13 is turned off, and the transistor 3 is turned offbecause its base is grounded. The transistors 3 and 8 and the neon bulb13 remain in the above state even when the switch 1 is kept closed.

Therefore, whenever the switch 1 is closed, one rectangular waveformvoltage as shown in FIG. 2 is generated, and the neon bulb 13 conductsduring the pulse duration T of this pulse voltage, so that the capacitor16 is charged through the input resistor 14. In this case,

the gate voltage V of the field-effect transistor 15 is given by where Evoltage after the neon bulb 13 conducts;

R resistance of the input resistor 14; and

C capacitance of the capacitor 16.

Since the pulse duration T is dependent upon the time constant which isdependent upon the values of the resistor 11 and the capacitor 9, therise of the gate voltage V is dependent upon the time constant, which inturn is dependent upon the values of the input resistor 14 and thecapacitor 16. The drain current of the MOS field-effect transistor 15 isin proportion to the gate voltage V until the field-effect transistor 15is saturated, so that the output voltage which is the product of thedrain current and the value of the output resistor 17 is also inproportion to gate voltage V Therefore, the output voltage derived fromthe output terminal 18 is increased stepwise whenever the switch 1 isclosed as shown in FIG. 3.

FIG. 3 shows the number of switch closings, spaced along the horizontalaxis of the graph by a fixed, arbitrary distance that does not take intoaccount the time between switch closings.

To return the output voltage to zero, the gate voltage V is decreased tozero.

Second Embodiments, FIGS. 4 and 5 Next referring to FIG. 4 illustratinga circuit diagram of the second embodiment of the present invention, thebase of a transistor 21 of a monostable multivibrator generallyindicated by is connected through a resistor 22 and a switch 19 to thepositive terminal of a power source 23, and a resistor 24 connects thejunction between the resistor 22 and the switch 19 to ground. The baseof the transistor 21 is also connected through a resistor 25 to thecollector of the other transistor 26. The collectors of the transistor21 and 26 are connected through resistors 28 and 30, respectively, to apositive DC power source +V and their emitters are grounded. The base ofthe transistor 26 is connected through a resistor 29 to the DC source +VThe collector of the transistor 21 is connected through a capacitor 27to the base of the transistor 26, and the collector of the transistor 26is connected through a neon bulb 31 and an input resistor 32 to the gateof a MOS field-effect transistor 33. The gate of the field-effecttransistor 23 is connected through a control resistor 37 and a neon bulb38 to a negative power source V, and is grounded through a non-polarizedcapacitor 34. The drain of the transistor 33 is connected to a DC powersource +V and the source is grounded through an output resistor 35, andis connected to an output terminal 36.

Next, the mode of operation will be described. When the switch 19 isopened, the transistor 26 is turned on so that its collector potentialis substantially equal to zero. Therefore, the neon bulb 31 does notconduct. When the switch 19 is closed, the current flows into the baseof the transistor21 through the resistor 22 so that the transistor 21 isturned on. The collector potential drops to zero so that the basepotential of the transistor 26 also drops to zero. As a result, thetransistor 26 is turned off so that its collector potential rises to alevel substantially equal to +V thereby raising the neon bulb 31 to itsfiring potential and causing it to conduct. The base potential of thetransistor 21 gradually rises with a time constant which is dependentupon the values of the resistor 29 and the capacitor 27, and thetransistor 26 is turned on. Then, its collector potential drops to aboutzero so that the neon bulb 31 is turned off, and the transistor 21 isturned off, since the base of the transistor 21 is almost grounded. Thetransistors 21 and 26 and the neon bulb 31 remain in the above stateseven when the switch 19 is kept closed. That is, whenever the switch 19is closed, one rectangular waveform voltage as shown in FIG. 2 isgenerated, and the neon bulb 31 conducts during the pulse duration T, sothat the capacitor 34 is charged through the input resistor 32. The gatevoltage V is given by where E voltage after the neon bulb 31 conducts;

R resistance of the resistor 32; and

C capacitance of the capacitor 34.

The pulse duration T is dependent upon the values of the resistor 29 andthe capacitor 27, so that the rise of the gate voltage V is dependentupon a time constant which is determined by the values of the resistor32 and the capacitor 34. The drain current of the MOS fieldeffecttransistor 33 is in proportion to the gate voltage V so that the outputvoltage which is the product of the drain current and the value of theoutput resistance 35 is also in proportion to the gate voltage V Thus,the output voltage derived from the output terminal 36 is increasedstepwise whenever the switch 19 is closed as shown in FIG. 5.

Since the neon bulb 38 is connected to the negative voltage source, itconducts when the voltage across the capacitor 34 and hence the gatevoltage V rises in excess of a predetermined level, so that thecapacitor 34 is discharged through the resistor 37 and the neon bulb 38.Therefore, the voltage across the capacitor 34 drops. When the voltageacross the capacitor 34 drops to a predetermined level which is lowerthan the firing voltage of the neon bulb 38, the discharge of thecapacitor 34 is stopped, and the voltage across the capacitor 34 is suchthat the pinch-off of the field-effect transistor 33 takes place. Theabove steps are cycled whenever the switch 19 is closed as shown in FIG.5.

Third Embodiment, FIGS. 6, 7 and 8 In the third embodiment shown in FIG.6, one terminal of a neon bulb 51 is connected to two monostablevibrators generally indicated by 40 and 58, respectively, andsubstantially similar in construction, except that the monostablemultivibrator 40 uses NPN transistors 41 and 46, while the monostablemultivibrator 58 uses PNP transistors 59 and 64. Therefore, it willsuffice to describe only the arrangement of the monostable vibrator 40,which is also substantially similar in construction to the monostablemultivibrator 20 shown in FIG. 1.

The base of the NPN transistor 41 is connected through a resistor 42 anda switch 39 to the positive terminal ofa power source 43, and a resistor44 connects ground to the junction between the resistor 42 and theswitch 39. The base of the'transistor41 is also connected through aresistor 45 to the collector of the NPN transistor 46, and the base ofthe transistor 46 is connected through a capacitor 47 to the collectorof the transistor 41. The transistors 41 and 46 have their collectorsconnected through resistors48 and 50, respectively, to a positive DCvoltage source V and their emitters grounded. The bases of thetransistor 46 is connected through a resistor 49 to the source V Thecollector of the transistor 46 is connected to one terminal of the neonbulb 51 whose the other terminal is connected through an input resistor52 to the gate of a MOS field-effect transistor 53. A non-polarizedcapacitor 54 connects ground to the gate of the MOS field-effecttransistor 53. The drain of the field-effect transistor 53 is connectedto a positive DC voltage source V while the source is connected to anoutput terminal 56, and is grounded through an output resistor 55.

In the monostable multivibrator 58, the base of the PNP transistor 59 isconnected through a resistor 60 and a switch 57 to the negative terminalof a power source 61, and the collectors of the transistors 59 and 64are connected through resistors 66 and 68, respectively, to a negativeDC voltage source V and their emitters are grounded. The base of thetransistor 64 is connected through a resistor 67 to the source -V Next,the mode of operation will be described hereinafter. When the switch 39of the monostable multivibrator 40 is opened, the transistor 46 conductsso that its collector voltage is almost equal to zero. Therefore, theneon bulb 51 is not conducting. When the switch 39 is closed, thecurrent flows into the base of the transistor 41 through the resistor 42so that the latter is turned on. The collector voltage drops to almostzero so that the base potential of the transistor 46 also drops toalmost zero and the transistor 46 is turned off. Therefore, thecollector potential of the transistor 46 approaches +V so that the neonbulb 51 conducts.

The base potential of the transistor 46 gradually increases with a atime constant which is dependent upon the values of the resistor 49 andthe capacitor 47, and the transistor 46 is turned on. Then, thecollector potential of the transistor 46 drops to almost zero so thatthe neon bulb 51 is turned off. The transistor 41 is turned off becauseits base is almost grounded. The transistors 41 and 46 and the neon bulb51 remain in the above states even when the switch 43 is kept closed.That is, when the switch 39 is closed, the rectangular waveformcollector voltage as shown in FIG. 2 is generated. The neon bulb 51conducts during the pulse duration T so that the capacitor 54 is chargedthrough the input resistor 52. The gate voltage V of the MOSfield-effect transistor 53 is given by V =E (1 e 3 where E voltage afterthe neon bulb 51 conducts; R resistance of the resistor 52; and Ccapacitance of the capacitor 54.

The'pulse duration'T is dependent upon a time constant which isdetermined by the values of the capacitor 47 and the resistor 49 so thatthe rise of the gate voltage V is dependent upon the time constant whichis de- 5 pendent upon the values of the resistor 52 and the capacitor54. Since the drain current of the MOS fieldeffect transistor 53isinproportion to the gate voltage, the output voltage which is theproduct of the drain current and the resistance of the output resistor55 is also in proportion to the gate voltage. Therefore, the outputvoltage derived from the output terminal56 is increased stepwisewhenever the switch 39 is closed.

When the switch 57 is closed, the transistor 64 is turned off so thatits collector potential drops to almost -V Therefore, the rectangularwaveform negative voltage as shown in FIG. 7 is generated at thecollector of the transistor 64. As a result, the capacitor 54 isdischarged so that the gate voltage of the MOS field-effect transistor53 drops by a predetermined level. Therefore, the output voltage alsodrops stepwise.

As described hereinbefore, the output voltage increases stepwisewhenever the switch 39 is closed while whenever the switch 57 is closed,the output voltage drops stepwise. FIG. 8 shows the output voltage whichis increased stepwise by three steps and then decreased stepwise bythree steps, but it is understood that the output voltage may beincreased and decreased in any step.

What is claimed is:

1. A device for generating variable output voltage comprising a. a MOSfield-effect transistor,

b. a non-polarized capacitor connecting the gate of said MOSfield-effect transistor to ground,

c. a neon bulb,

d. an input resistor connected in series with the neon bulb,

e. a monostable multivibrator means connected to the gate of said MOSfield-effect transistor through said input resistor and said neon bulbfor providing a single square wave output pulse in response to an inputsignal, said square wave output pulse having a predetermined electricalpotential and a duration sufficient only to charge said non-polarizedcapacitor through said input resistor and said neon bulb to a potentialthat is less than one-half the predetermined electrical potential.

f. a switch connected to said monostable multivibra- 5O tor means forproviding said input signal, and

g. an output resistor connecting the source of said MOS field-effecttransistor to ground, whereby when said switch is repeatedly closed, theoutput voltage derived from the source of said MOS fieldeffecttransistor increases stepwise. 2. A device for generating variableoutput voltage as defined in claim 1 wherein said monstablemultivibrator comprises a pair of PNP transistors. 3. A device forgenerating variable output voltage as defined in claim 1 wherein thegate of said MOS field-effect transistor is connected through a controlresistor to a second neon bulb, whereby an output voltage whichincreases stepwise to a predetermined level by a predetermined number ofsteps and then falls to zero may be repeatedly generated.

4. A device for generating variable output voltage as defined in claim 1further comprising I a second monostable multivibrator means comprisinga pair of transistors of one conductivity type wherein the firstmonostable multivibrator means comprises a pair of transistors of theopposite conductivity type, a switch connected to the base of one ofsaid pairs of transistors of said second monostable multivibrator means,and the collector of the other transistor of said second monostablemultivibrator means being connected to said one terminal decreasedstepwise.

1. A device for generating variable output voltage comprising a. a MOSfield-effect transistor, b. a non-polarized capacitor connecting thegate of said MOS field-effect transistor to ground, c. a neon bulb, d.an input resistor connected in series with the neon bulb, e. amonostable multivibrator means connected to the gate of said MOSfield-effect transistor through said input resistor and said neon bulbfor providing a single square wave output pulse in response to an inputsignal, said square wave output pulse having a predetermined electricalpotential and a duration sufficient only to charge said non-polarizedcapacitor through said input resistor and said neon bulb to a potentialthat is less than one-half the predetermined electrical potential. f. aswitch connected to said monostable multivibrator means for providingsaid input signal, and g. an output resistor connectiNg the source ofsaid MOS fieldeffect transistor to ground, whereby when said switch isrepeatedly closed, the output voltage derived from the source of saidMOS field-effect transistor increases stepwise.
 2. A device forgenerating variable output voltage as defined in claim 1 wherein saidmonstable multivibrator comprises a pair of PNP transistors.
 3. A devicefor generating variable output voltage as defined in claim 1 wherein thegate of said MOS field-effect transistor is connected through a controlresistor to a second neon bulb, whereby an output voltage whichincreases stepwise to a predetermined level by a predetermined number ofsteps and then falls to zero may be repeatedly generated.
 4. A devicefor generating variable output voltage as defined in claim 1 furthercomprising a second monostable multivibrator means comprising a pair oftransistors of one conductivity type wherein the first monostablemultivibrator means comprises a pair of transistors of the oppositeconductivity type, a switch connected to the base of one of said pairsof transistors of said second monostable multivibrator means, and thecollector of the other transistor of said second monostablemultivibrator means being connected to said one terminal of said neonbulb, and a second switch for providing an input signal to said secondmonostable multivibrator means, whereby when the switch of one of saidfirst and second monostable multivibrator means is closed, the outputvoltage may be increased stepwise while when the switch of the othermonostable multivibrator means is closed, the output voltage may bedecreased stepwise.